The epidermal growth factor receptor (EGFR) is an important target forthe treatment of head and neck squamous cell carcinoma (HNSCC). Clinical strategies to target EGFR have focused on monoclonal antibodies (mAbs), such as cetuximab. Cetuximab executes its antitumor effect in vivo via blockade of receptor-ligand interactions and engagement of Fcgamma receptors on immune effector cells which trigger antibody-dependent cell-mediated cytotoxicity (ADCC). Our preliminary studies demonstrate that tumor cell-autonomous expression of TGF-beta is a key molecular determinant of the de novo or acquired resistance of cancers to EGFR-targeted mAb, and provide a rationale for enhancing the antitumor efficacy of anti-EGFR mAb by combinatorial- or bi-functional antibody-based strategies to simultaneously counteract TGF-beta in the tumor microenvironment. The aims of the project are designed to advance the clinical translation of this strategy for treatment of HNSCC; Specific Aim I: Determine whether tumor cell-autonomous expression of TGF-beta inhibits cetuximab-induced ADCC in patients with HNSCC. Specific Aim II: Determine the in vivo antitumor efficacy and toxicity of dual blockade of EGFR and TGF-beta using HNSCC patient-derived tumor xenografts in mice. Specific Aim III: Determine the clinical relevance of TGF-beta as a molecular determinant of resistance to cetuximab in patients with HNSCC, and evaluate the clinical safety of a novel bi-functional anti-EGFR antibody that can sequester and block TGF-beta in the tumor microenvironment. This project addresses the urgent need for effective tumor-targeted therapeutic strategies against HNSCC by: (1) Establishing the role of tumor cell-autonomous expression of TGF-beta as a key mechanism and clinical biomarker of resistance to cetuximab in patients with HNSCC; (2) Improving the treatment of patients with HNSCC and other cancers via novelcombinatorialor bi-functional antibody-based strategies that simultaneously target and counteract EGFR and TGF-beta in the tumor microenvironment. The project will leverage the expertise and resources of the JHU Tissue Core, Biostatistics Core, and will interact with Projects 1 and 4 of the SPORE-Head and Neck Cancer.